An inert gas such as helium, argon, krypton, or nitrogen, and other types of gases have been widely used in electronics industry. Examples of such inert gases used in an electronics field include a gas used in a semiconductor production process itself and a general-use gas used as a purge gas or a dilution gas in an each step. In these gases, the required level of purity largely varies according to an each step, and in the case of the use in a semiconductor production process, the ultrahigh purity is required, in which each of the impurity contents in a gas is 1 ppb or less.
Examples of the components which should be removed as impurities in a gas used in a semiconductor production process include oxygen, carbon dioxide, carbon monoxide, hydrogen, water, nitrogen oxide, and hydrocarbons. In the case where inert gases are to be purified, nitrogen and xenon become objects to be removed in addition to the aforementioned impurities.
Conventionally, in order to remove these impurities and to obtain a purified gas, a getter method is used, which mainly uses a chemical reaction with a highly active getter material. This method is excellent in that each of impurities can be removed to thereby reduce the total content thereof to 1 ppb or less. However, since a getter material cannot be regenerated, it has to be renewed when the life time thereof is expired. Furthermore, since the reaction is performed at a high temperature, the running cost is high. In addition, when impurities of a high content, for example several hundreds ppm, are contaminated in a gas to be purified, a getter material is overheated by the heat of reaction, and in the worst case, there is a problem that a getter material is melted down.
The present inventors have previously found that zeolite, which contains a cupper ion and has a specific crystal structure (ZSM-5 type) (hereinafter, may be referred to as “Cu-ZSM5 zeolite”), is capable of adsorbing and removing these impurity components and of being regenerated by heating, and that a regeneratable purifier can be realized by using this Cu-ZSM5 zeolite (for example, see Patent Reference 1).
By the way, when an adsorbent is used in an industrial plant, it must be a molded product in order to reduce pressure loss. Examples of a molded product include a product granulated in a spherical or pellet shape and a product integrally molded in a porous shape. However, in the case where Cu-ZSM5 zeolite is molded to be a molded product, the problem that the adsorption capacity to trace impurities is largely decreased in comparison with zeolite powder of a raw material was found.
In order to mold zeolite, a small amount of an organic binder is used in addition to an inorganic binder such as kaolin, attapulgite, montmorillonite, bentonite, allophane, or sepiolite. It was speculated that these binders have an effect on the decrease of adsorption capacity. However, there were few documents which describe a method of activating a molded product of Cu-ZSM5 zeolite.
In the present invention, the term “activation” is different from a regeneration treatment of an adsorbent, and means developing the adsorption performance, which an adsorbent originally possesses, by performing a treatment once before the use of an adsorbent.
A general method of activating Cu-ZSM5 zeolite is a method in which a heat-treatment is performed in air or an inert gas such as nitrogen or vacuum after Cu ion exchange. For example, as an improved example of the activation of Cu-ZSM5 zeolite, the method is effective, in which Cu-ZSM5 zeolite is heat-treated in nitrogen dioxide-containing air to thereby produce an oxidizing combustion catalyst of a hydrocarbon and an oxygenated hydrocarbon (for example, see Patent Reference 2). This treatment is performed for the purpose of increasing the ratio of Cu2+ ions which is useful in an oxidation reaction.
In addition, as another activation method, the method is disclosed, in which Cu-ZSM5 zeolite of a catalyst for exhaust gas purification is heat-treated at a temperature of 500° C. to 500° C. in the mixed gas in which hydrogen is added to argon or nitrogen for example, see Patent Reference 3). This method is for obtaining a special dispersion state of Cu2+ and Cu+.
In addition, as another activation method, the method is disclosed, in which Cu-ZSM5 zeolite is heat-treated under the special condition of a carbon monoxide atmosphere at a temperature of 150° C. to 500° C. to thereby produce a carbon monoxide adsorbent (for example, see Patent Reference 4). It is disclosed that this heat-treatment enables reducing Cu2+ ions to Cu+ ions.
The pentasil-type zeolite in which Cu ion exchange is performed is known as a nitrogen oxide adsorbent for a pressure swing adsorption method. The technique is disclosed, in which a heat-treatment is performed in a helium atmosphere at 500° C. (for example, see Patent Reference 5).
In Japanese Unexamined Patent Application, First Publication No. Hei 1-96010, the method of producing the molded product of Cu ion-containing zeolite is disclosed, and the heat-treatment following Cu ion exchange is performed at a temperature of 500° C. in the flow of a helium gas (for example, see Patent Reference 6).
None of the aforementioned references disclose a treating method aimed at the activation of a molded product.    [Patent Reference 1] Japanese Unexamined Patent Application, First Publication No.    [Patent Reference 2] Japanese Examined Patent Application, Second Publication No. Sho 57-36015    [Patent Reference 3] Japanese Unexamined Patent Application, First Publication No. Hei 3-65242    [Patent Reference 4] Japanese Unexamined Patent Application, First Publication No. Sho 60-156548    [Patent Reference 5] Japanese Unexamined Patent Application, First Publication No. Hei 5-76751    [Patent Reference 6] Japanese Unexamined Patent Application, First Publication No. Hei 1-96010